In the ITU-R (International Telecommunication Union Radio communication sector), a standardization work for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the third generation) is in progress. IMT-Advanced sets its goal to support IP (Internet Protocol)-based multimedia service at the data transfer rate of 1 Gbps in stop and slow-speed moving states and of 100 Mbps in a fast-speed moving state.
One of the powerful candidates as system standards to fulfill the requirements of IMT-Advanced is LTE-A (Long Term Evolution-Advanced) of 3GPP (3rd Generation Partnership Project). The LTE-A is an improved version of 3GPP LTE (hereinafter referred to as ‘LTE’). The LTE is part of E-UMTS (Evolved-UMTS) using an E-UTRAN (Evolved-Universal Terrestrial Radio Access Network). The LTE adopts OFDMA (Orthogonal Frequency Division Multiple Access) in downlink and SC-FDMA (Single Carrier-Frequency Division Multiple Access) in uplink.
In the LTE-A, consideration is taken of a relay station to be included in a wireless communication system. The relay station functions to extend the cell coverage and improve transmission performance. A base station can have an advantage of extending the cell coverage by servicing user equipments, located in the cell coverage thereof, through relay stations. Further, since the relay stations improve transmission reliability between the base station and the user equipments, the transmission capacity can be increased. A relay station may be utilized in the case in which a user equipment is located in a shadow region although it is within the coverage of a base station.
A relay station commonly divides subframes into a reception subframe for receiving a signal from a user equipment connected thereto and a transmission subframe for transmitting a signal to a base station in order to prevent self-interference. Here, a guard time needs to be placed in the reception subframe or the transmission subframe of a signal. The guard time is used for stabilization and the prevention of interference according to the transmission/reception switching of a signal in a relay station. If the guard time is included in the transmission subframe, available time resources that the relay station can transmit a signal to the base station are reduced.
Further, during the time for which a relay station receives a signal from a user equipment connected to the relay station (hereinafter referred to as a ‘R-UE’), it is difficult for the relay station to transmit a signal to a base station. In the case in which a signal transmitted by a R-UE is received in some of the transmission subframes of a relay station because of, for example, propagation delay, the relay station may not use some of the transmission subframes.
Meanwhile, in a wireless communication system environment, fading is generated because of multi-path time delay. A process of restoring a transmission signal by compensating for the distortion of a signal, occurring because of an abrupt change in the environment due to fading, is called channel estimation. In general, channel estimation is performed using a reference signal (RS) known to both a receiver and a transmitter. A relay station can also transmit the reference signal to a base station.
Further, a relay station may need to transmit control information such as channel information between a base station and the relay station, ACK/NACK (acknowledgement/not-acknowledgement), to a base station.
In the case in which a relay station transmits a reference signal or a backhaul UL signal, such as control information, to a base station, there is a need for a signal transmission method in which a reduction in available time resources in the backhaul uplink between a relay station and a base station due to a guard time or the reception of a signal from a R-UE is taken into consideration.